The present invention relates to an information recording medium, an information recording and reproducing method, and an information recording medium producing method. More particularly, the present invention relates to an information recording medium which has an information recording layer consisting of a dispersion type of liquid crystal and which enables information to be recorded thereon as visible information by exposure carried out under voltage application or by application of a voltage, and also relates to an information recording and reproducing method for such an information recording medium and to an information recording medium producing method.
In conventional electrophotographic technology, an information recording medium is known which comprises a liquid crystal cell having a nematic liquid crystal material sealed therein that is stacked on a photoconductive layer, an insulating layer for liquid crystal alignment that is stacked on the liquid crystal cell, and a pair of electrodes that sandwich the cell structure. To record information, the information recording medium is exposed to information light under application of a voltage between the electrodes, thereby lowering the resistance of the photoconductive layer at regions exposed in the pattern of the applied information light, aligning the liquid crystal molecules in the exposed regions, and thus obtaining a visible image by using a polarized light plate.
The known information recording medium necessitates formation of a cell for sealing a liquid crystal therein. In addition, it is necessary in order to effect initial twisted nematic alignment to provide insulating films which have been subjected to alignment treatment by rubbing or the like on both surfaces of the cell, and it is also necessary to mix the liquid crystal material with a spacer in order to maintain the cell gap at a constant level. For these reasons, the conventional information recording medium cannot obtain images of high resolution. Further, since rigid and transparent substrates are needed to provide a gap or to form a cell, optical problems are associated with the prior art. There is another problem in that the information recording medium which has been subjected to alignment treatment in its initial state needs a polarized light plate to detect the recorded information.
In the meantime, an information recording medium in which a polymer dispersed liquid crystal is used as a liquid crystal layer in the liquid crystal cell has recently been developed. In such an information recording medium, the liquid crystal layer is sandwiched between two substrates having ITO electrodes. However, if this information recording medium is arranged in a structure comprising a substrate, an ITO electrode, and a liquid crystal layer and it is used in an information recording method wherein exposure is carried out under voltage application with the information recording medium placed face-to-face with a photosensitive member, thereby recording electrostatic information on the liquid crystal layer by an electric discharge phenomenon occurring in accordance with the information light applied thereto, the polymer dispersed liquid crystal may ooze out on the surface of the liquid crystal layer, resulting in noise that affects the information recording operation.
In a case where an ITO electrode is formed directly on a liquid crystal layer to realize an arrangement that comprises a substrate, an ITO electrode, a liquid crystal layer, and an ITO electrode and where a voltage is applied between the two electrodes to align the molecules in the liquid crystal layer to thereby record information, the ITO electrode on the surface layer may be cracked or raised by oozing of the liquid crystal, resulting in a lowering in the electrical conductivity. In addition, when an electrode layer and a liquid crystal layer are formed by laminating, problems arise in terms of the uniformity of the gap and the noise induced by the spacer.
Further, in a case where a smectic liquid crystal is dispersed in the resin material, the memory effect is particularly good, so that even after the removal of the electric field, the modulated molecular alignment is maintained as it is; even if the information recording medium is left to stand for a long time, the recorded information can be read. Since the recorded visible image can be erased by heating the information recording medium to a temperature near the isotropic phase transition temperature, the information recording medium can be reused.
However, if information is recorded on the information recording layer of an information recording medium that employs such a liquid crystal by carrying out exposure under voltage application with the information recording medium placed face-to-face with a photosensitive member, the liquid crystal may ooze out on the surface of the information recording layer, resulting in noise that affects the information recording operation. It is also difficult to maintain the gap between the photosensitive member and the information recording medium at a constant level.
Incidentally, a liquid crystal recording medium is suitable for use in the form of a card, a disk, a film, etc. because it enables the recorded information to be optically read with ease. In such applications, it is desirable to fix the gap between the photosensitive member and the liquid crystal recording medium by forming them together as one unit. In the case of such a card type liquid crystal recording medium, it is necessary to form a transparent electrode or the like on the information recording layer. However, since the information recording layer, which comprises a liquid crystal dispersed in a resin material, is soft, it is difficult to form an electrode on the information recording layer, and the recording layer is likely to be damaged. In addition, the information recording layer involves the above-described problem of oozing of the liquid crystal. In particular, when the liquid crystal recording medium is placed under severe environmental conditions where it is touched with human hands as in the case of a card or a disk, the liquid crystal recording medium is likely to be damaged or deformed, which results in noise that affects the reliability of the data. Accordingly, it is extremely important to eliminate such a cause of noise when the liquid crystal recording medium is used as a card. It has also been demanded to develop a technique of continuously producing card type liquid crystal recording media.
It is an object of the present invention to provide an information recording medium which enables information to be recorded with high accuracy without using a liquid crystal cell and which allows easy reproduction of the recorded information, and also provide an information recording and reproducing method for such an information recording medium. More particularly, it is an object of the present invention to provide an information recording medium which is free from unevenness of recorded information which would otherwise be caused by oozing of a polymer dispersed liquid crystal when used as an information recording layer, and also to provide an information recording and reproducing method for such an information recording medium and an information recording medium producing method.